Apparatus for use in color



Feblll, 1936. E. GRE TENER APPARATUS FOR USE IN COLOR PHOTOGRAPHY FiledDec. 23, 1933 III Patented Feb. 11, 1936 UNITED] STATES,

PATENT OFFICE.

APPARATUS FOR USE COLOR RAPE! PHOTOG Edgar Gretener,Berlin-Si'emcnastadt,

Germany,

assignor to opticolorAktiengesellschatt, Giana, Switzerland, acorporation of Switaer 1 Application December 2:, 193:, Serial at. massIn Germany, December 29, 1932 objective which reproduces the originalfilm on the duplicate film and which is provided with a specialdiaphragm. This diaphragm is seen from the films in the same distancesas the multicolor screens are seen when the views are taken orprojected. The opening of the diaphragm is divied-by stripeswhichconceal those regions of the aperture of the copying objectivewhich correspond to the borders between adjacent zones 01' themulticolor screen. As, generally, the images on the original film arepositive ones, got by inversal, the said diaphragm decreases the lightdifiusion .from one color to the other ones.

This invention relates to an improvement of the apparatus used in theabove described wellknown printing process and particularly of thediaphragms used for performing the same. It was found that the images onthe duplicate film are better and have better colors when the diaphragmis so constructed that some symmetry conditions are fulfilled- As alwaysthe light which passes a region corresponding to one zone of themulticolor screen,

'of the emulsion on the original film is scattered so that difi'uselightaiso passes the other zones and as this defect may not be whollysuppressed even by the use of diaphragms or the known type, it isnecessary for getting nevertheless good projected images to take carethat the diflfusions are symmetrical for the different colors. The saiddii'iusions occur also-in the taking and projecting process. They couldbe. suitably shaped multicolorscreens which would,

however, cause great losses 01' light. So all un-' symmetricaldiflusions the copying process easily be balanced copying process.

The details of the invention may be explained by thehelp oi the annexeddrawing of which Fig. 1 shows a sectional view of a copying device,

Fig. 2 the front view 01 a diaphragm or the new yp I Fig. 3 the frontview of a diaphragm used for constructing the diaphragm ot- Figure 2,

Figure 4 a sectional viewot a part of a lenticulated film,

' Fig. 5 some curveswhich represent the transparencies' of the emulsionlayer,

I are compensated for by as then losses of light may by lowering thespeed 01 the and which is similarly shown in'Fig. 5.

given by the curved line 01' Fig. 5 instead of the 2 Claims. (Cl. 88-24)Fig. 6 a sectional view of a part of a lenticulated film and the path01' the light beams Referring first to Fig. 4 there are drawn thelentic'ular elements I, I, and I". In the emulsion 5 layer behind eachlens three zones 2, 3, l or 2', I,

l or 2", 3f, 4" are corresponding to the respective zones of themulticolor screen which was emthrough it.

'ployed in a well-known manner when the film was exposed, It is assumedthat the three ditferently colored zones are of equal width, so thatalso the widths 01 the Stripes 2, I, l, 2', 3', l,

I" I", I" are equal. Aslt is preferable when the dimensions are chosenin this manner-the following explanations are based upon thispresumption without being necessarily restricted toit.

When now a view is taken on the film,

layer is after the reversal process partly trans-- parent. If the takenobject is colored so that its light rays only pass through one zone oithe filter, the transparencies of the layer ought to,

be represented by the line of Fig. 4, which rises rectangularly over thezones 2, '27, I" and so on,

It is known that an improvement may be got by arranging a diaphragm inthe photographic objective concealing the borders between thefilter-zones. Then the real transparencies are theoretical broken line.The maxima of the curved line of Figure 5 are more distinct and sharperthan'those of the corresponding curve of Figure 4. But their height islowered from which iac t results that the concealing must not be toomuch augmented.

-The circumstances are similar in the projection process. There toolightedifiusing occurs which produces color degradatlons.- Also thiseilect may be, at least partially, compensated for. by the meetdiaphragms which, however, reduce the luminosity. The result of thedescribed dili'usion is that the colors seem to be pale and that nointense and deep colors may be got. 11" for instance a film is-proiectedwith a concealed red zone which was taken through, a filter withconcealed blue and green zones, there ought to be, in contradiction tothe experimental result, no light on the projection screen. In co oi thelight-diffusion the red color loses its saturation and seems pale. Thepoint or the color triangle which represents the red got by projectingan exposed film is displaced towards white.

An utmost disturbing effect or the difiusion which is to be avoided bythe invention consists in the fact that the degradation of the colors isof unsymmetrical manner. Generally the diffusion from one marginal zoneto the other one is much weaker than from .one marginal zone to thecentral zone or from the central zone to one marginal zone. Theconsequence is that some colors can not be projected in any satisfactorymanner while other colors which are of smaller importance are nearlycorrectly projected. If for-instance the central zone is red and themarginal ones green and blue, the efiective red on the projection screenis much more degradated towards white than blue and green as thelight-diffusion between the central zone and the two lateral zones israther strong, the

diffusion from green to blue and from blue to green being weak.Sometimes it is even possible that the very white point is lying nearthe borders of triangle formed by the effective projection colors. Thenit is not possible to get pure white.

Such lack of symmetry must be avoided. A

condition for this aim is to give the zones an equal breadth. Furtherthe unsymmetry has its j origin in a light-scattering by theneighbouring lenticular elements and in the circular shape of themulticolor screen which causes the central zone to touch the lateralones by long straight lines while the two marginal zones, beingcurveshaped at their outer borders, are only touching each other in onepoint when they are periodically repeated as is affected by thelenticular elements. Both reasons may be described in full detail by thehelp of Figures 2 and 6.

Fig. 6 refers to the case that the lenticular film of which a smallpiece has been drawn in sectional view is illuminated from theunembossed side and that a projection objective with the multicolorscreen is arranged on the lenticulated side. Then conically shapedlight-bundles of the angular opening a pass through all points of thelayer; That light-cone which passes through the center of the zone 3reaches as a whole the lenticularelement l and is refracted in such amanner that it passes through the center of the multicolor screen. Onthe contrary, only a part of the other light cone'which passes throughthe zone 2 represented in Figure 6 reaches the lenticular element I,another part of considerable value striking the lenticular ele- Thislast named part is so refracted ment i.

that it does not reach the objective. So only a part of the lightreaches that zone of the screen corresponding to the zone 2. Thereforethe intensity of the light decreases more and more towards the marginsof the lenticular'elements and the most intense difiusion occurs betweenthe central and the lateral zones but not between the. lateral ones.

This effect of light-scattering by the neighbouring elements isaugmented by another one, which may be explained with respect to Figure2.

This figure shows a front-view of the plane of the diaphragm which maybe employed for projection purposes. following explications, if thefilms are projected on a screen or if they are projected on another filmfor reproducing the record. Even, in the taking process similaranomalies occur.

when a film withcylindrically shaped lenticular elements runningparallel to the strip is projected with the help of an objective whichhas a circular aperture as is drawn in the figure, each vertical smallstrip of the aperture is passed by jection objective,

It is without influence in the a certain quantity of light being afunction of the situation of said strip. It is small at the sides andgreat at the center. The reason is not only the light scattering by theneighbouring lenticuiar elements but also the circular shape of theaperture. The integral quantity of light passing by the zone 5 may, forinstance, be tested/and drawn as ordinate. When this is done for thewhole breadth of the aperture, the dashed line 6 is got. This is afurther reason for the fact that the diffusion between the central andthe lateral zones is much greater than the dlflusionbetween the twomarginal zones. Such a degradation of colors occurs in every projectionprocess, for producing a cinematographic view as well as for drawingduplicates. It may be considerably decreased by shaping the aperture ofthe copying objective as is represented in Figures 1 and 2.

In Figure 1 the film I3 is to be reproduced, while the film ll is to beexposed by the help of the objective l5 which contains a diaphragm l6,represented in Figure 2 in front view. It is seen from the films at theplanes II or 18 which have from the films the same distances as theimages of the corresponding images in the taking or projecting process.The film I3 is lighted by a light source l9 and a condenser 20.

The aperture of the objective is divided into three stripes of equalbreadth by the lines I and 8. The diaphragm I6 is placed within theobjective and conceals the lines 1 and 8. It has three apertures. Theseare the unhatched areas in Figure 2, viz. the two diangles 8 and I0 andthe central rectangle ii. The apertures are so shaped that the centersof gravity of the three transparencies. on the duplicate film are lyingat equal distances from each other. For this purpose the areas 9 and Illare so shaped that their centers of gravity have a distance from thecenter of the aperture ll greater than one third of the diameter. Bythis means a duplicate film is got which is characterized by the factthat the stripes behind the lenticular elements have equal distancesfrom each other though these stripes are drawn towards the centralstripe behind each lens on the original film.

It is even possible and has proved of high importance for practical workto use a diaphragm tween the central andthe lateral zones is alreadycompensated for. projected colors may, wholly symmetrical.

It therefore a screen is used, the central zone being red and the twoothers blue and green,

, the lack of saturation by additions of white is for all colors thesame. Each of the three colors gets the same percentage of whiteaddition. Only the addition to blue may sometimes be somewhat greaterwithout being observable.

The exact shape of the diaphragms may be got by pure calculations. Butit is more preferable to use a diaphragm of approximately the correctshape and to improve it by some as the stronger diifusion be-Thedegradations of the by this means, he made iii aosaaaeresentedinFigureS. Thebreadthoi'thisaperture must be equal to that o!the projection objective and have the same distance from the film,including the action of the optical system. Now the intensities of lightpauing through the.

threezones aretestedbyconcealingtwoaones and leaving the third open. Theproportions oithethreeintensitiesareailmctlcndthecdor degradatiombylight-diil'usion.

This experiment is twice repeated whereby in the taking process theother cones remain open. Having at last got the proportions tor theblue, red and green monochrome it is easily seen itthedegradationsarethesameiorredgrem and blue. or, ii not, in what mannerthe diaphragm o! the printing objective must be changed for equalizingthem.

Then another duplicate is drawn from the original with the new diaphragmand the degradations are once more tested. After some steps the correctdiaphragm is got.

Itisalsopossible-toexposeanoriginalillm through the open takingobjective directed to-, wards a white object. The duplicate drawn fromsuch original with the help or the diaphragmed printing objective isprojected and the intensities of light passing through small stripes ofthe'pro jection objective parallel to the lenticulations are tested.Thusthecurve i2 oi'l'lgure3isgot corresponding to curve l of Figure 2.Itis assumed that the duplicate is drawn with the helpotatalsediaphragmsothattlnmaximaotcm-ve'samestepsmaybetakenwiththeonlydiilerenee gradations oi color the thatthe correct projection system is used its testingthedmadaticns.Itisprelerabletocombinewiththeeilecto! thenewprintingdia.torendereoualdseil'ect that the stripesbehind a lenticular element haveequal whenawhiteorgreycbjectwas taken-Thisccnsiderablydecreasuthetmdencytocolordominantsinthelight'anddarkparts ottheviews.Generallmtorthispurpoaathecentralsonemustbesmallerthanthelateralones.

'Ihenewapparatusisnotlimitedtothreeaones.'lhereareoniysmallalterationswhichareeasilytakenbyanybodylearnedinthearhwhenmorethanthreescnesotthreeormorethan threeeolorsare used.'lhen,too.thecolordegradationsmustbeequal.

Iclaim:

l. Inan optical system for use with lenticulated illms having threecolorrecords behind each lenticuiatiom'a illm sate through whichv suchaillmisadaptedtobemoved,adiaphragm throughwhichli'ghtmaypasstoori'romsaidillm in the gate-means to form an image of saiddiaphragmatsaidgatdsaiddiaphragmhaving three apertures spaced aparttransversely o! the lenticulationson thefllm, thecentral one 0! saidaperturesbeingrectangui'arinshapeandtheside aperturesbeingseparatediromthe central aperturebymstripssaidstrlpshavingcurved edges iorming theboundaries or said side aper-' diaphragm at said gate, said diaphragmhaving thre'eaperturesspacedaparttransvenelyoi'the lenticulationson-thefllm,the centralone oi said apertures being rectangular in shapeand the side-apertures being separated from the central aperture byopaque strips said strips havingcurvededgeaiormingtheboundariesoi'saidsideapertureaandthecentersotgravltyoi'saldapertures being equallyspaced fromeach other.

